In rolling of metal or alloy rods, metal stock is passed progressively through a series of rolls which encourage the plastic flow of metal causing length extension and transverse area reduction of the stock.
The mill rolls are subjected in use to arduous conditions of heat, pressure, and friction.
In copper rolling to produce stock for wire production the mill rolls are cylindrical typically having a diameter of about 220 mm and a width of 100 mm, that is to say, a width much greater than the rolled stock. As one part of the roll circumference becomes excessively worn, another part is brought into use.
When as a result of wear, no further part of the roll surface is satisfactory, the roll surface is machined.
The costs of roll installation, roll refurbishing, and mill down time neccessitated by the wear of mill rolls, together with costs of the inventory of mill rolls required, are substantial.
Hitherto, mill rolls have been manufactured from tool steel. Steel is readily machinable before and after wear. It has a sufficient coefficient of friction to roll copper without undue slippage. It is able to withstand thermal and mechanical shock and it is sufficiently robust and resistant to fracture for use in a mill environment.
Ceramics such as zirconia, silicon nitride, silicon carbide, alumina and others are known to have high strength and wear resistance and for these reasons have been used as hot metal extrusion dies. To date no such materials have been successfully used for mill rolls because the difficulty and cost of fabricating a conventional mill roll wholly from ceramics renders the use of ceramics uneconomical for the purpose and also because ceramics are relatively susceptible to fracture and thermal shock under conditions to which mill rolls are subjected. More particularly it has not hitherto been thought practicable to manufacture an object of the size, mass and precision of a mill roll for copper rolling from ceramics.
An object of the present invention is to provide an improved mill roll.
A further object is to provide a mill roll having a ceramic working surface and which is of acceptability low cost and/or high durability.
According to one aspect the present invention consists in
a mill roll comprising a hub and a ceramic annular formulation sleeved upon the hub to provide a mill roll working surface.
In preferred embodiments the ceramic annular formation has side walls extending at an angle to the hub radial direction and is clamped to the hub by clamping means engaging the side walls and maintaining the formation under compression.
An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings wherein